Directional electromagnetic ratio calibration
AssigneeSchlumberger Technology Corporation
InventorsMark Frey, Dean Homan
Life of this patent
Estimating the term…
Abstract
A method for making calibrated directional electromagnetic logging measurements includes causing an electromagnetic logging tool to make a plurality of voltage measurements while deployed in a subterranean wellbore. A ratio of currents in first and second electromagnetic transmitters is computed and a ratio of gains in first and second electromagnetic receivers is computed. A ratio of selected ones of the measured voltages is processed in combination with the ratio of currents, the ratio of gains, and a test loop calibration coefficient to compute the calibrated directional electromagnetic logging measurement.
Claims17
A method for making a calibrated directional electromagnetic logging measurement, the method comprising:
- deploying a tool in a subterranean wellbore, the tool including first and second electromagnetic transmitters and first and second electromagnetic receivers;
- causing the tool to make a plurality of measurements while deployed in the subterranean wellbore, each of the plurality of measurements including a voltage measured at one of the first and second electromagnetic receivers when one of the first and second electromagnetic transmitters fires;
- performing a downhole calibration of the first and second electromagnetic transmitters and the first and second electromagnetic receivers, the downhole calibration including computing a ratio of currents in the first and second electromagnetic transmitters and a ratio of gains in the first and second electromagnetic receivers;
- and
- processing a ratio of selected ones of the measured voltages in combination with the ratio of currents, the ratio of gains, and a test loop calibration coefficient to compute the calibrated directional electromagnetic logging measurement.
An electromagnetic logging tool comprising:
- a logging tool body;
- first and second transmitters deployed on the logging tool body;
- first and second receivers deployed on the logging tool body and spaced apart from the first and second transmitters;
- a processor configured to:
- cause the first and second transmitters and the first and second receivers to make a plurality of measurements while the electromagnetic logging tool is deployed in a subterranean wellbore, each of the measurements including a voltage measured at one of the first and second receivers when one of the first and second transmitters fires;
- perform a downhole calibration of the first and second transmitters and the first and second receivers, the downhole calibration including computing a ratio of currents in the first and second transmitters and a ratio of gains in the first and second receivers;
- and
- process a ratio of selected ones of the measured voltages in combination with the ratio of currents, the ratio of gains, and a test loop calibration coefficient stored in memory to compute a calibrated directional electromagnetic logging measurement.
Dependencies are inferred from the claim text.